carbon; and also by Dr. Zenker, who replaced the liquid in M. Jamin's construction by wedges of flint glass.

The following tabular view of different forms of polarizing prisms is taken from the conclusion of Dr. Feussner's paper :

As an analysing prism of about 6 mm. clear width, and 13.5 mm. long, the new prism is stated by its inventor to be of the most essential service, and it would certainly appear that the arrangement is rather better adapted for small prisms than for those of considerable size. Any means by which a beam of polarized light of large diameter-say 3 to 3 in.- could be obtained with all the convenience of a Nicol would be a real advance, for spar of sufficient size and purity for such a purpose has become so scarce, and therefore so valuable, that large prisms are difficult to procure at all. So far as an analyser is concerned, the experience of Mr. P. R. Sleeman would lead to the opinion that improvements are to be looked for rather in the way of the discovery of an artificial crystal which absorbs one of the polarized rays than by further modifications depending upon total reflection. The researches of Dr. Herapath on iodosulphate of quinine are in this direction; but crystals of

*

* Phil. Mag., 1852, p. 161, and 1853, p. 346.

the so-called herapathite require great manipulative skill for their production. If these could be readily obtained of sufficient size, they would be invaluable as analysers.

This opinion is supported by the existence of an inconvenience which attends every form of analysing prism. It is frequently, and especially in projecting apparatus, required to be placed at the focus of a system of lenses, so that the rays may cross in the interior of the prism. This is an unfavourable position for a prismatic analyser, and in the case of a powerful beam of light, such as that from the electric arc, the crossing of the rays within the prism is not unattended with danger to the cementing substance, and to the surfaces in contact with it.

Abbe's Analysing Eye-piece.-This (fig. 74), devised by Prof.

FIG. 74.

Abbe, consists of a Huyghenian eye-piece with a doubly refracting prism P (a calc-spar prism achromatized by two suitable glass prisms) inserted between the eye-lens O and fieldlens C, and over the diaphragm at B. The rays polarized parallel to the refracting edge pass through the prisms without deviation, whilst those polarized at right angles are strongly deflected, and are stopped off by a diaphragm over the eye-lens. The field of view remains undiminished.

Measurement of the Curvature of Lenses.* -With very small lenses the spherometer cannot be used, and Prof. R. B. Clifton's method is based on the Newton's rings formed between the lens and a plane surface, or a curved surface of known radius. From the wave-length of the light employed in observing and the diameter of a ring the radius of curvature can be determined. He places the lens on a plane or curved surface under a Microscope, and lights it by the sodium flame -wave-length 5892 x 10-7-measures the approximate diameters of two rings a distance apart (in practice the tenth and twentieth rings are found convenient), takes the difference of their squares, and divides it by the wave-length and the number of rings in the gap between to find the radius of the lens. The formula is :

115

where + and x, are the diameters of the nth and (m + n)th rings; A is the wave-length of the light, and p' the radius of curvature of the lens. The method with proper care gives accurate results. Prof. Clifton has also used it to determine the refractive index of liquids in

* Nature,' xxix. (1883) p. 143.

1.3335

small quantities; Mr. Richardson having found it for water by this method, which is usually correct to two places of decimals. It can also be used to determine if the lens is uniformly curved and spherical.

New Microscopical Journals. Two new Journals have made their appearance. The first is the quarterly 'Zeitschrift für wissenschaftliche Mikroskopie und für mikroskopische Technik,' published at Brunswick, and edited by Drs. L. Dippel, M. Flesch, A. Wichmann, and W. J. Behrens. It embraces "Microscopy" in its widest sense, and includes original articles, abstracts and reviews, and a bibliography of microscopical literature. It may be recommended to all microscopists who read German. The other is the bi-monthly 'Microscopical Bulletin,' published by Queen and Co., of Philadelphia, which, though unpretentious, gives useful information on microscopical subjects.

Eye-pieces and Objectives.

[General explanations.]

The Microscope, IV. (1884) pp. 105-6.

The Microscope, IV. (1884) pp. 107-12.

Bausch and Lomb Optical Co.'s Improved "Investigator" Stand.

[Cf. I. (1881) p. 100. Mirror and substage now swing independently, position of body-rack changed, &c.] Amer. Mon. Micr. Journ., V. (1884) p. 84 (1 fig.). BOHN, C.-Ueber die Berichtigung des vereinfachten Ablese-Mikroskopes für Theilungen. (On the rectification of the simplified reading Microscopes for graduations. [Supra, p. 436.]

Zeitschr. f. Instrumentenk., IV. (1884) pp. 87-8.

BOND, G. M.-Standards of Length and their Subdivision.
[Describes the Saxton Yard-dividing Comparator, the Rogers-Bond Universal
Comparator, and a Comparator made by the Ballon Manufacturing
Company for Professor Anthony.]

Journ. Franklin Institute, CXVII. (1884) pp. 281-95, 357-67 (5 figs.). BRADBURY, W.-The Achromatic Object-glass. XXXII.-V.

Engl. Mech., XXXIX. (1884) pp. 93-4, 159–60, 246-7, 272 (6 figs.). "CALCULUS.”—Polarizer for the Microscope. [Simple contrivance to fit on tail-piece.]

Engl. Mech., XXXIX. (1884) p. 215 (1 fig.). CONGDON, E. A.-Microscopy one hundred and fifty years ago. [Notes on 'Baker on the Microscope,' 1740.]

D., E. T.-Graphic Microscopy.

The Microscope, IV. (1884) pp. 74-6.

IV. Pollen of Mallow. V. Peristome of Fumaria hygrometrica.
Sci.-Gossip, 1884, pp. 73–4 (1 pl.), 97–8 (1 pl.).

DAVIS, G. E.-[Leitz's] Oil-immersion Objectives.

Micr. News, IV. (1884) pp. 131-2.

Evenings with the Microscope. I.

[Measuring magnifying power of objectives and eye-pieces, and testing corrections of objectives.]

Micr. News, IV. (1884) pp. 132-5.

Sci. Monthly, I. (1883) p. 26.

FLESCH, M.-Welche Aussichten bietet die Einführung des elektrischen Lichtes in die Mikroskopie? (What prospect does the introduction of the electric light afford in Microscopy?) [Post.] Zeitschr. f. Wiss. Mikr., I. (1884) pp. 175–81. HANSEN, E. C.- Ueber das Zählen mikroskopischer Gegenstände in der Botanik. (On the counting of microscopic objects in Botany.) [Post.]

Zeitschr. f. Wiss. Mikr., I. (1884) pp. 191-210 (6 figs.). HAZLEWOOD, F. T.-A home-made revolving Table. [Post.]

Amer. Mon. Micr. Journ., V. (1884) p. 94.

HITCHCOCK, R.-Neglected Opportunities. [Exhortation to investigate the microscopic life of the country.] Amer. Mon. Micr. Journ., V. (1884) pp. 95-6.

A New Microscopical Society.

Sarcastic comment on the announcement of the establishment of the Ladies' Microscopical Society at San Francisco having been first sent to England. “Trusting the members will learn that, although they may look to foreign lands for styles and methods of personal adornment, when they come to such a serious subject as microscopy, their wants can be as well met and their fame as well appreciated in their own country."]

Amer. Mon. Micr. Journ., V. (1884) p. 97.

JADANZA, N.—Sui sistemi diottrici compositi. (On compound dioptric systems.) Atti R. Accad. Sci. Torino, XIX. (1883) pp. 99-117. JUNG, H.-Ueber ein neues Compressorium. (On a new Compressor.) [Post.] Zeitschr. f. Wiss. Mikr., I. (1884) pp. 248-50 (2 figs.).

LANCASTER, W. J.-Lantern Microscope.
[Directions for making. "You may make a lantern Microscope in half a
dozen different ways, and the method to work upon will depend entirely
upon the illumination you have. You state in query that you have the
lime-light; you could not have anything better. Fit up your Microscope
in any form you like, and for object-lenses get three sets of lenses, A, two
1 in. focus, both plano, one 1/2 in., the other 3/4 in. diameter; B, two
lenses both 1 in. focus, one 3/8 in. diameter, the other 5/8 in. diameter;
C, two lenses 3/4 in. focus, one 1/4 in., the other 1/2 in. diameter; and
D, two lenses 1/2 in. focus, one 3/16 in., the other 3/8 in. diameter.
Mount them in separate tubes in each case, both convex surfaces together,
at the following distances apart:-A 1 in., B 2/3 in., C 1/2 in., D 5/16 in.;
then a stop must be placed in front of each of the smallest lenses, the
larger lens going towards object. The sizes of stops and their distances
from small lenses are as follows:-A, 1/8 in. diameter, 1/2 in. in front;
B, 3/32 in., 5/16 in.; C., 1/12 in., 3/16 in.; D, 1/16 in., 1/8 in."]
Engl. Mech., XXXIX. (1884) p. 152.
LOMMEL, E.-Spectroskop mit phosphorescirendem Ocular. (Spectroscope with
phosphorescent eye-piece.) [Post.]
SB. K. Akad. Wiss. München, 1883, p. 408.
Micr. Bulletin, I. (1884) p. 23.

Magnifying Powers, Table of, with Note.
MCCALLA, A.-The "Congress" Nose-piece.
[Reply to Mr. Bulloch, ante, p. 300, with woodcuts of his original design.]
Amer. Mon. Micr. Journ., V. (1884) pp. 64–5 (3 figs.), 78–9.
The Microscope, IV. (1884) pp. 101-2.

MERCER, F. W.-A New Photomicrographic Camera. [Post.]

Photography (Chicago), I. (1884) pp. 9-10 (1 fig.).

MITCHELL, G. O.-A Focusing Glass for Photo-micrography. [Post.]

Amer. Mon. Micr. Journ., V. (1884) p. 80 (1 fig.).

NELSON, E. M.-On the selection and use of Microscopical Apparatus. [Ante, p. 302, repeated here to give the following note:-(1) The Ross is decidedly to be preferred to the Jackson form, mainly on the ground of

the superiority of the long lever fine-adjustment over any other. (2) No Microscope is worthy to be called a scientific instrument unless it has a centering substage. (3) Choice and Aperture of Objectives, supra, p. 447. (4) Eye-pieces. (5) Daylight, artificial light, and incandescence lamp, supra, p. 447. (6) Condensers (Powell's the most effective for powers beyond 1/4). (7) Paraboloids, Lieberkuhns (post), Vertical Illuminator, and Micrometers. (8) Polarization. (9) Diffraction and the difficulties of interpretation with objects requiring high magnification.]

Engl. Mech., XXXIX. (1884) p. 48.

NOE, L. H.-Homogeneous immersion. ["It seems to me that to make a lens which shall work through different thicknesses of cover-glass equally well and without adjustment, the immersion medium should correspond with the cover-glass, so that the combined thickness of glass and immersion fluid would always be the same (although the thickness of each varied) for an object in contact with the under side of the cover."]

Amer. Mon. Micr. Journ., V. (1884) p. 79.

"NOT AN OPTICIAN."-Theory of the Achromatic Object-glass. [Comments on O. V.'s articles.]

Eng. Mech., XXXIX. (1884) p. 210.

"ORDERIC VITAL."-The Dialyte and Plate Glass.

Engl. Mech., XXXIX. (1884) p. 215. ORTH, J.--Cursus der normalen Histologie zur Einführung in den Gebrauch des Mikroskopes sowie in das practische Studium der Gewerbelehre. (Course of normal Histology as an introduction to the use of the Microscope as well as to the practical study of Histology.) 3rd ed., xii. and 340 pp., 108 figs. 8vo, Berlin, 1884. PEAUCELLIER.-Note sur la déformation des images réfractées et sur l'aplanatisme d'un système de lentilles. (Note on the distortion of refracted images and on the aplanatism of a system of lenses.)

Mém. Soc. Sci. Bordeaux, V. (1883) pp. 327-34 (1 pl.). PERAGALLO, H.-Histoire sommaire du Microscope composé et de ses récents perfectionnements. (Compendious history of the compound Microscope and its recent improvements.) 8vo, Toulouse, 1883.

PLERN, F.-Apparat zur Prüfung der Brennweite des Auges oder anderer optischer Systeme. (Apparatus for testing the focal length of the eye or other optical systems.)

Title only of German Patent, Cl. 42, No. 1894, Feb. 1884. "PRISMATIQUE."-Plate Glass for Optical Purposes.

Engl. Mech., XXXIX. (1884) pp. 191-2, 281. PROCTOR, R. A.-Review of Poulsen and Trelease's Botanical Micro-chemistry,' in which the invention of the achromatic microscope-objective is attributed to J. J. Lister in 1829! Knowledge, V. (1884) p. 231.

PUSCHER & WIEDERHOLD.-Cementing Brass on Glass. [Puscher recommends a resin soap for this purpose, made by boiling 1 part of caustic soda, 3 parts of colophonium (resin) in 5 parts of water and kneading into it half the quantity of plaster of Paris. This cement is useful for fastening the brass tops on glass lamps, as it is very strong, is not acted upon by petroleum, bears heat very well, and hardens in onehalf or three-quarters of an hour. By substituting zinc white, white lead, or air-slaked lime for plaster of Paris, it hardens more slowly. Water only attacks the surface of this cement. Wiederhold recommends, for the same purpose, a fusible metal composed of 4 parts of lead, 2 parts tin, and 2 parts bismuth, which melts at 212° Fahr. The melted metal is poured into the capsule, the glass pressed into it and then allowed to cool slowly in a warm place.]

Polyt. Notizblatt. See Engl. Mech., XXXIX. (1884) p. 119. REICHERT, C.-Anleitung zum Gebrauche des Mikroskops. (Introduction to the use of the Microscope.) 14 pp. (2 figs.), 8vo, Wien, 1883.

Ser. 2.-VOL. IV.

2 I